1. Field of the Invention
The present invention relates to a developing device, a process cartridge, and an image forming apparatus, and more particularly relates to a developing device that uses Electrostatic Transport & Hopping (ETH) and that can obtain high developing efficiency with low voltage drive, a process cartridge and an image forming apparatus that includes this developing device.
2. Description of the Background Art
Image forming apparatuses such as copying machines, printers, or facsimile machines use a xerographic process to form a latent image on an latent image carrying member. A powder developer (hereafter referred to as toner) is applied to the latent image to develop the latent image so that a toner image is made visible. This toner image is transferred onto a recording medium, or temporarily transferred onto an intermediate transfer member before being transferred onto the recording medium, to form images.
In this type of image forming apparatus, it is known that conventionally in the developing device that develops latent images formed on the latent image carrying member, toner that is agitated within the developing device is carried on the surface of a developer carrying member, or a developing roller. By rotating the developing roller the toner is transported to a position in opposition to the surface of the latent image carrying member, and the latent image on the latent image carrying member is developed. Then after completion of developing, toner that has not been transferred to the latent image carrying member is recovered within the developing device by the rotation of the developing roller. Then toner is newly agitated, charged, and again transported by being carried on the developing roller.
Also, as disclosed in Japanese Patent Application Laid-open No. H9-197781 and Japanese Patent Application Laid-open No. H9-329947, conventional image forming apparatuses are known which develop using the so-called jumping developing method. In this type of image forming apparatus DC and AC superimposed voltages are applied between the latent image carrying member and the developing roller. The toner is then transferred from the developing roller to the latent image carrying member without contact.
Further, as disclosed in Japanese Patent Application Laid-open No. H5-031146, Japanese Patent Application Laid-open No. H5-031147, and elsewhere, other conventional image forming apparatuses have been proposed in which toner is transported to a position in opposition to the latent image carrying member using an electrostatic transport substrate. The toner is vibrated, suspended, and aerosolized, and separates from the transport surface due to the force of attraction between the toner and the latent image carrying member and adheres to the surface of the latent image carrying member. Also, as disclosed in Japanese Patent Application Laid-open No. H8-003673, image forming apparatuses that obtain color images by superimposing toner in many colors onto the latent image, in which the method of making the toner jump from the developing roller is used are known. Also, as disclosed in Japanese Patent Application Laid-open No. H3-021967, image forming apparatuses have been proposed in which superimposed developing is carried with toner that has been suspended by the electric field curtain effect.
However, in image forming apparatuses having a developing device that provides toner to the latent image carrying member using a developing roller as described above, toner penetrates between the developing roller and the side plate of the developing device, causing rubbing and accretion of toner. This can adversely affect images, as the sealant material around the developing device deteriorates with age, and images become dirty due to suspension of toner caused by agitation and charging of developer or toner within the developing device.
Also, when toner is charged by friction charging or corona discharge charging, toner that is a mixture of saturated charged toner and unsaturated charged toner is obtained, that has a large charge distribution. If this kind of toner is forcibly transferred to the developing roller using a magnetic brush or transfer roller, some of the toner with a small charge that is carried on the developing roller separates from the developing roller, due to the developing speed (linear speed about 100 cm/sec.) of the developing roller. As a result toner becomes suspended, and the images formed can become dirty.
Further, in developing devices that use so-called jumping development, toner charged by a high voltage must be provided. Therefore, a high voltage source is required, which can create the problems of increasing the size of the device and increasing the cost. Also, the current problem for image forming apparatuses using powder is how to satisfy the requirements of image quality, cost, and environment.
Also, when forming a color image, for image quality 1200 dpi isolated dots of only 30 μm diameter must be formed. For this purpose also it is desirable that developing be carried with no dirt. Further, reducing cost is important, not just the cost of the developing unit and the toner, but also the total cost including maintenance and final disposal cost. Also, for the environment it is important to prevent toner which is a fine powder from being dispersed within or outside the device.
Technologies relating to the present invention are also disclosed in, for example, Japanese Patent No. 3,376,199.